UPDATED: Amgen's osteoporosis drug 'romo' comes through with promising PhIII

Amgen's Sean Harper

Amgen scored promising Phase III data for its osteoporosis drug romosozumab, providing a pivotal win for the Big Biotech's late-stage pipeline and moving the drug one giant step toward an FDA filing later in the year. But some analysts were quick to note that at first blush the drug didn't perform as well as its main late-stage rival at Radius Health, triggering concerns about how well it may perform if it makes the leap to the market.

Amgen ($AMGN) and its partner UCB noted that co-primary endpoints on reducing spine (or vertebral) fractures among postmenopausal women suffering from osteoporosis were achieved along with a secondary endpoint for lowering the number of all fractures--though it missed another secondary on significantly reducing nonvertebral fractures. 

Researchers found that the women taking the injectable experienced a 73% reduction in risk for spine fractures and a 36% reduction in risk for all clinical fractures compared to the placebo arm. And the effect persisted in the second year of treatment as patients were transitioned to Prolia (denosumab).

Analysts have been carefully tracking romo, pegging this as a potential blockbuster with peak sales potential north of $1 billion a year. At the same time it's been compared with Radius Health's ($RDUS) abaloparatide, which achieved an even higher 86% reduction in spine fracture risk compared with a placebo. Radius' drug is a daily injectable while Amgen's drug is injected once a month, which could give the Big Biotech a distinct edge.

Radius' shares soared 26% in early trading, though, while Amgen's edged up slightly, a clear indication of investors' sentiments at this stage of the game.

"Optically, we believe these data (for romo) came in below investor expectations, caveat that we don't have the detailed fracture data and tough to compare across trials," noted Evercore ISI's Mark Schoenebaum, who also flagged concerns about two cases of osteonecrosis of the jaw as well as one atypical femoral fracture in the romo group. Radius execs told him no comparable safety threats were revealed in their study.

Radius also had to endure some criticism for its decision last fall to delay a regulatory filing until 2016, in part due to its decision to be respectful of employees' holiday plans. That didn't sit well with some, who expected to see a more aggressive posture from a company engaged in a Phase III development race with a big player like Amgen.

For Amgen, romo offers a chance to follow up on its big PCSK9 drug approval, offering investors fresh evidence of the productivity of its R&D group, which has been called into question time and again in recent years.

The experimental drug romo is an antibody designed to block the protein sclerostin. Researchers say that it has the ability to both build bone and prevent its breakdown. And the data will likely win over analysts comparing this drug to Eli Lilly's ($LLY) Forteo, which is going generic. Amgen reported last fall that romo beat Forteo (which earned $1.3 billion) in a head-to-head study. A separate Phase III comparing romo to Fosamax is underway and due to read out in 2017, well after this drug may hit the market.

"Assuming the data are competitive, we think romo will be commercially attractive given its monthly dosing, its differentiated data on cortical bone, and potentially the lack of a black box warning for osteosarcoma that is on Forteo's label (and likely abaloparatide's)," noted UBS's Matthew Roden in a preview of the results.

"A vertebral fracture due to osteoporosis can be a life-altering event, and the risk of these kinds of fractures will be a growing burden as our society ages," said Dr. Sean Harper, executive vice president of research and development at Amgen. "These data show that romosozumab reduced new vertebral fracture risk as soon as 12 months."

- here's the release